The present invention relates to retroreflective sheeting with an image and more specifically a validation image.
Validation images have been used for years for authentication and security purposes. A watermark is an identifying pattern or legend either on or in a material to provide validation of the material. Retroreflective sheeting with directional and non-directional watermarks have been used as a validation means for documents, phonographs, cassette tapes, compact disk containers, traffic signage and license plates.
One problem with watermarks on retroreflective material is providing the watermark in a manner which provides the needed authentication but which provides some subtlety or inconspicuousness, such as being discernable in only a few angles of viewing. Expensive processing steps and equipment are often required to provide such a watermark. Additionally, there is generally little processing control over the conspicuousness or intensity of the watermark.
It is desirable to have an image that is distinct and viewable for authenticating purposes. Further, it is desirable to have a processing means to provide the desired intensity of the image. It is also desirable to have an image that is subtle and directional.
This invention relates to retroreflective sheeting that has an image, such as a validation image. In one embodiment, the image is directional having varying appearance at different angles of view.
The retroreflective sheeting comprises a layer of transparent microsphere lenses, a transparent polymeric spacing layer having a front surface and a back surface wherein the spacing layer is underlying, contacting, and substantially conforming to the bottom of the lenses, and the spacing layer comprises one or more segments having a refractive index different from the refractive index of the remainder of the spacing layer, a reflective layer having a top surface and a bottom surface wherein the top surface is in contact with the back surface of the spacing layer, and a topcoat cover sheet overlying and conforming to the top surfaces of the lenses and having a flat top surface or face. In another embodiment, the retroreflective sheeting includes a pressure sensitive or thermally activated adhesive layer underling and in contact with the bottom surface of the reflective layer. The retroreflective sheeting has an image whose proportions are determined by the variation of refractive index of the one or more segments from the refractive index of the remainder of the spacing layer, and by its conformation to the bottom of the lenses. The image of the present invention can range from conspicuous to inconspicuous and directional to non-directional.